1. Field of the Invention
The present invention relates to an electric power steering apparatus, and more particularly, to a fail-safe function of electric power steering for automobiles, etc. using a multi-phase motor with three or more phases such as a DC brush-less motor.
2. Description of the Prior Art
FIG. 16 is a block diagram showing a conventional electric power steering apparatus disclosed in the Japanese Patent laid-Open no. 1-257674. In FIG. 16, reference numeral 11 denotes a steering torque detector; 12, a torque signal input I/F circuit; 13, a microcomputer (CPU); 14, a motor rightward drive output I/F circuit; 15, a motor leftward drive output I/F circuit; 16, a D/A conversion circuit; 17, a differential amplification circuit; 18, a pulse width modulation circuit; 19, a PWM oscillator (OSC); 20, a motor drive circuit; 20A and 20B, AND circuits; 21, a motor current detection circuit; 22, a resistor; 23A and 23B, output terminals; 24, a motor; 25A and 25B, input terminals; 26, a motor control circuit; 27, a motor rotation drive judging block; 27A, a torque signal direction discrimination circuit; 27B, a rightward drive signal; and 27C, a leftward drive signal.
Here, the motor rotation drive judging block 17 constructs a redundant system independent of the microcomputer 13, which is the main motor controlling means. The motor rotation drive judging block 27 decides the right or left direction of the steering torque of the driver detected by the steering torque detector 11 through the torque signal direction discrimination circuit 27A and if the steering torque is rightward, allows rightward powering of the motor 24 by the motor drive circuit 20 through the rightward drive signal 27B. If the steering torque is leftward, the motor rotation drive judging block allows leftward powering through the leftward drive signal 27C.
Conventionally, a single-phase motor with a brush has been used for an electric power steering apparatus. In recent years, however, there is a demand for a more comfortable steering feeling to such an extent that friction of the brush is no longer negligible. Thus, use of a brush-less multi-phase motor, such as a three-phase DC brush-less motor for an electric power steering apparatus is under investigation.
When a single-phase motor with a brush is reversibly operated with an H-figured bridge circuit, ON/OFF of each switching element making up the H-figured bridge circuit has a one-to-one correspondence with the output torque direction of the motor. Thus, as described above, the conventional electric power steering apparatus is provided with redundant means for turning ON/OFF the switching elements according to the direction of steering torque in parallel to the main controlling means such as a microcomputer in the control apparatus and drives the motor using a logic product of the main controlling means by the redundant means. Even in the case where the main controlling means fails, this prevents the motor from generating steering auxiliary torque in the direction opposite to the steering torque or generating steering auxiliary torque when the steering torque is close to a neutral point.
On the other hand, in the case of a multi-phase motor, ON/OFF of each switching element making up the motor drive circuit does not have a one-to-one correspondence with the output torque direction of the motor. For example, in the case where a three-phase DC brush-less motor is driven by a three-phase inverter, all switching elements making up the three-phase inverter can be either ON or OFF no matter which direction of torque the motor outputs. For this reason, there is a problem that the redundant means of the conventional apparatus cannot be used.
The present invention has been implemented to solve the problem as described above and it is an object of the present invention to provide a highly reliable electric power steering apparatus incorporating a microcomputer redundant system also applicable to electric power steering using a multi-phase motor.
The electric power steering apparatus according to the present invention comprises a multi-phase motor that assists steering effort of a driver, driving means provided with at least an upper switching element that connects or disconnects the winding of each phase of the multi-phase motor and a power supply, and a lower switching element that connects or disconnects the winding of each phase of the multi-phase motor and grounding and a logic circuit that determines ON/OFF of the upper switching element and the lower switching element and first and second controlling means for controlling the driving means via the logic circuit, and characterized in that the logic circuit determines ON/OFF of the upper switching element and the lower switching element so that the power to the winding of the each phase is stopped according to the instruction of either the first control means or the second control means.
This configuration makes it possible, in an electric power steering apparatus using a multi-phase motor such as a three-phase DC brush-less motor, to construct a microcomputer redundant system that controls the motor with an extremely small amount of calculation and produces thereby an effect of improving the reliability of the apparatus.
The electric power steering apparatus according to an alternative embodiment of the present invention comprises a torque sensor that detects the steering effort of the driver, and is characterized in that the torque sensor is connected to both of the first controlling means and the second controlling means, or the torque sensor is connected to the first controlling means and the first controlling means is connected to the second controlling means to send a value of steering torque detected by the torque sensor to the second controlling means.
This configuration produces an effect of contributing to construction of a redundant system with a microcontroller appropriate for electric power steering with an extremely small amount of calculation, and also produces an effect of making it possible to implement strict monitoring with a simpler hardware configuration.
In another configuration of the electric power steering apparatus according to the present invention, the apparatus comprises a motor current detection circuit that detects a current of the multi-phase motor, and is characterized in that the motor current detection circuit is connected to both of the first controlling means and the second controlling means, or the motor current detection circuit is connected to the first controlling means and the first controlling means is connected to the second controlling means to send a detected current based on a target current at three-phase AC coordinates or a detected current based on the current detection circuit to the second controlling means.
This configuration produces an effect of contributing to construction of a redundant system with a microcontroller appropriate for electric power steering with an extremely small amount of calculation, and also produces an effect of making it possible to construct a redundant system with a microcontroller that controls the motor of the electric power steering apparatus using the multi-phase motor.
Another electric power steering apparatus according to the present invention comprises a rotor position sensor that detects the position of the rotor of the multi-phase motor, and is characterized in that the rotor position sensor is connected to both of the first controlling means and the second controlling means, or the rotor position sensor is connected to the first controlling means and the first controlling means is connected to the second controlling means to send the detected position based on the position sensor to the second controlling means.
This configuration produces an effect of contributing to construction of a redundant system with a microcontroller appropriate for electric power steering with an extremely small amount of calculation, and also produces an effect of making it possible to construct a redundant system with a microcontroller that controls the motor of the electric power steering apparatus using the multi-phase motor.
Further, the electric power steering apparatus according to the present invention can comprise a speed sensor that detects the rotation speed of the rotor of the multi-phase motor, and is characterized in that the speed sensor is connected to both of the first controlling means and the second controlling means, or the speed sensor is connected to the first controlling means and the first controlling means is connected to the second controlling means to send the detected position based on the position sensor to the second controlling means.
This configuration produces an effect of contributing to construction of a redundant system with a microcontroller appropriate for electric power steering with an extremely small amount of calculation, and also produces an effect of making it possible to construct a redundant system with a microcontroller that controls the motor of the electric power steering apparatus using the multi-phase motor.
In another embodiment, the electric power steering apparatus according to the present invention comprises a vehicle speed sensor that detects the traveling speed of the vehicle on which the electric power steering apparatus is mounted, and is characterized in that the vehicle speed sensor is connected to both of the first controlling means and the second controlling means, or the speed sensor is connected to the first controlling means and the first controlling means is connected to the second controlling means.
This configuration produces an effect of contributing to construction of a redundant system with a microcontroller appropriate for electric power steering with an extremely small amount of calculation.
Additionally, the electric power steering apparatus according to the present invention may have the logic circuit constructed to turn OFF at least one of the upper switching element and the lower switching element based on the instruction of either the first controlling means or the second controlling means.
This configuration makes it possible to reduce the circuit scale of the logic circuit, simplify the circuit configuration and contribute to cost reduction and also produces an effect of constructing a microcomputer redundant system that controls the motor of the electric power steering apparatus using a multi-phase motor.
In another alternative embodiment, the electric power steering apparatus according to the present invention may have the driving means including at least an upper switching element that connects or disconnects the winding of each phase of the multi-phase motor and a power supply, a lower switching element that connects or disconnects the winding of each phase of the multi-phase motor and grounding and switching means for connecting or disconnecting the upper or lower switching element and a power supply or grounding, and is characterized in that the logic circuit is constructed to turn OFF the switching means based on the instruction of either the first controlling means or the second controlling means.
This configuration produces an effect of interrupting power to the multi-phase motor reliably.
Further, the electric power steering apparatus according to the present invention may also have the driving means including at least an upper switching element that connects or disconnects the winding of each phase of the multi-phase motor and a power supply, a lower switching element that connects or disconnects the winding of each phase of the multi-phase motor and grounding and switching means for connecting or disconnecting the winding of each phase of the multi-phase motor and the upper or lower switching element, and is characterized in that the logic circuit is constructed to turn OFF the switching means based on the instruction of either the first controlling means or the second controlling means.
This configuration produces an effect of interrupting power to the multi-phase motor reliably.
Moreover, the electric power steering apparatus according to the present invention can be configured such that the first controlling means and the second controlling means are connected in such a way as to exchange predetermined data, monitor errors of each other based on the exchanged data and control the logic circuit in such a way as to interrupt the power to the multi-phase motor in the event of an error in the first or second controlling means.
This configuration produces an effect of allowing the first controlling means and the second controlling means to monitor each other for runaway.
Further, the electric power steering apparatus according to the present invention may be configured such that the second controlling means controls the logic circuit in such a way as to interrupt the power to the multi-phase motor in the case where the direction of steering torque does not match the direction of assisting steering effort, and to interrupt the power to the multi-phase motor in the case where steering torque is close to a neutral point whichever direction the steering effort of the driver is assisted.
This configuration produces an effect of making it possible to monitor the operation more strictly.
In a further alternative embodiment the electric power steering apparatus according to the present invention is characterized in that the second controlling means controls the logic circuit in such a way as to interrupt the power to the multi-phase motor in the case where the direction of steering torque does not match the direction of assisting steering effort, and not to interrupt the power to the multi-phase motor in the case where steering torque is close to a neutral point whichever direction the steering effort of the driver is assisted.
This configuration produces an effect of making it possible to monitor the operation more strictly, and also produces an effect of making it possible to drive the motor close to a neutral point of torque to compensate friction of the motor, etc. and improve the steering feeling.
Additionally, the electric power steering apparatus according to the present invention can be characterized in that the second controlling means controls the logic circuit in such a way as to interrupt the power to the multi-phase motor in the case where the motor output torque is excessive to the steering torque.
This configuration produces an effect of making it possible to monitor the operation more strictly.
In a further embodiment, the electric power steering apparatus according to the present invention is characterized in that the second controlling means controls the logic circuit in such a way as to interrupt the power to the multi-phase motor in the case where the relationship between the motor current at orthogonal coordinates and the motor current at three-phase AC coordinates is judged to be abnormal.
This configuration produces an effect of making it possible to construct a redundant system with a microcontroller that controls the motor of the electric power steering apparatus using the multi-phase motor.
The electric power steering apparatus according to a further alternative embodiment of the present invention is characterized in that the second controlling means controls the logic circuit in such a way as to interrupt the power to the multi-phase motor in the case where the relationship between the motor current at orthogonal coordinates, the motor current at three-phase AC coordinates and electrical angle is judged to be abnormal.
Additionally, the electric power steering apparatus according to the present invention may be characterized in that the second controlling means controls the logic circuit in such a way as to interrupt the power to the multi-phase motor in the case where the component of the motor current in the same direction as the magnetic flux created by the magnetic field is judged to be abnormal.
This configuration produces an effect of making it possible to construct a redundant system with a microcontroller that controls the motor of the electric power steering apparatus using the multi-phase motor.
The electric power steering apparatus according to yet another embodiment of the present invention is characterized in that the second controlling means controls the logic circuit in such a way as to interrupt the power to the multi-phase motor in the case where the phase angle formed by the current component of the motor current in the same direction as the magnetic flux created by the magnetic field and by the current component in the direction 90xc2x0 from the magnetic flux created by the magnetic field is judged to be abnormal.
This configuration produces an effect of making it possible to construct a redundant system with a microcontroller that controls the motor of the electric power steering apparatus using the multi-phase motor.
Alternatively, the electric power steering apparatus according to the present invention can be characterized in that the logic circuit is controlled in such a way as to interrupt the power to the multi-phase motor when the condition for interrupting the power to the multi-phase motor continues for a predetermined time.
This configuration produces an effect of making it possible to prevent hunting during power interruption.
In another exemplary embodiment of the electric power steering apparatus according to the present invention, when judged abnormal, the power to the multi-phase motor is interrupted until the first controlling means or the second controlling means is power-on reset.
This configuration produces an effect of making it possible to provide a fail-safe action until the second controlling means is recovered from the error.